1. Field of the Invention
The present invention relates to CCD sensors used for spectroscopy. In particular, the invention relates to a variable binning approach.
2. Description of Related Art
It is desired to provide a sensor that meets requirements for wide dynamic range detection over a wide spectral range at relatively high speed. Known approaches have tried to achieve these requirements using photo-multipliers, long integration timers, slow data readout or multiple exposure arrangements, all of which are quite costly.
U.S. Pat. No. 6,038,023 to Carlson et al. describes a programmable CMOS spectrometer which can be programmed to control spectral resolution. A set of pixels, not necessarily contiguous, or spectral bands are selected by writing a bit pattern to the control register that controls a switch so that photocurrents of the selected pixels are summed. U.S. Pat. No. 5,973,311 to Sauer, et al. describes an active pixel array with high and low resolution modes. In a low resolution mode, adjacent pixel elements, that are selected by row and column control lines, are coupled together through a switch to sum together their respective charges. However, the sensor resolution is not controlled by timing the reset of a sense node of a CCD readout structure.
U.S. Pat. No. 5,689,333 to Batchelder, et al. describes a spectrometer with a two dimensional CCD coupled to a computer for subsequent data processing. If the highest possible spectral resolution is not required, the software can use a technique called “binning,” in which several adjacent pixels are treated as a group. The software adds together the data which it captures from the consecutive pixels in the group, and treats the result as one data point.
U.S. Pat. No. 5,235,402 to Prytherch describes a spectrometer that uses a two dimensional CCD array where the output shift register is connected to an output circuit. Charges in the shift register are feed to a capacitor in the output circuit which can be periodically reset so that a standard CCD array can be tailored to the optical system used, and only those elements that are illuminated need be read out. However, the resetting is not controlled to enable the capacitor to integrate charges from a varying number of elements of the output shift register.
What is needed is wide dynamic range detection over a wide spectral range at relatively high speed at a relatively low cost.